The measurement of the lung function and especially the determination of the FRC during respiration (also known as ventilation) with the use of fluoropropane, namely, heptafluoropropane, hexafluoropropane or perfluoropropane as trace/tracer gases appears from DE 100 46 465 B4 and the equivalent U.S. Pat. No. 6,544,191 B2, so that reference is explicitly made to these prior publications for the method of lung function measurement and FRC determination (DE 100 46 465 B4 and U.S. Pat. No. 6,544,191 B2 are hereby incorporated by reference in their entirety).
A method for determining properties of the lungs outside of mechanical respiration by means of the bolus dosage of a mixture of different gases soluble in the blood, in which the measurement is evaluated by means of an optimization algorithm, for the expiratory gas concentrations measured subsequent to the inhalation, is described in U.S. Pat. No. 6,254,546 B1.
Moreover, various other trace gases have been used for the measurement of the FRC, these gases being added to the breathing gas, in general, in amounts of a few volume percentages (vol. %), as a result of which the harmful effect on the health of the patient being respirated and examined is very extensively reduced. The drawback of the trace/tracer gases used hitherto is the high purchase price and the generally great technical effort with which the trace gases used are filled and applied, with the consequence that diagnostic procedures for determining the lung function by means of trace gases have become established so far in niche markets only, such as high-performance sports medicine, and, in particular, they do not belong to the clinical routine in the case of mechanically respirated patients in intensive care units. Some trace gases, for example, helium, require, moreover, a great measuring technical effort due to the mass spectrometric determination to be used, and others, for example, sulfur hexafluoride, have no medical approval for medical use in most countries.